1. Field of the Invention
The present invention relates to a lens driving unit for sliding a lens group holding frame used in an imaging device, and a lens driving device for independently driving two lens groups.
2. Description of the Related Art
For a optical zooming system of an imaging device, a system in which two lens groups (a zooming lens group and a focusing lens group) are provided, and the system in which these lens groups are made to move in the optical axis direction has been applied. These two lens groups held in holding frames for holding the lens groups respectively are arranged in series so as to be able to slide in the optical axis direction.
To reduce size and weight of imaging device, for a lens driving device provided in a lens tube as well, a technology for reducing the size has been required. For example, in any of Japanese Patent Laid-Open No. 2005-17782, Japanese Patent Laid-Open No. 8-292358, Japanese Patent Laid-Open No. 2006-154373, Japanese Patent Laid-Open No. 8-271777, Japanese Patent Laid-Open No. 2006-64838, Japanese Patent Laid-Open No. 2002-131611 and Japanese Patent Laid-Open No. 2007-140396, size reduction in the width direction of the lens tube is achieved by gathering two driving mechanism parts (motor, lead screw) for driving two lens groups together on one side of the outside boundary of lens.    Japanese Patent Laid-Open No. 2005-17782    Japanese Patent Laid-Open No. 8-292358    Japanese Patent Laid-Open No. 2006-154373    Japanese Patent Laid-Open No. 8-271777    Japanese Patent Laid-Open No. 2006-64838    Japanese Patent Laid-Open No. 2002-131611    Japanese Patent Laid-Open No. 2007-140396
In recent years, for a high-performance lens having higher zooming ratio, size reduction has been required as well. However, to achieve a higher optical zooming ratio, the moving distances of a focusing lens and a zooming lens should be made long in general. Therefore, in reducing the size and weight of a lens having a high zooming ratio, the length in the optical axis direction of the lens driving device is physically restricted.
For example, in the technologies disclosed in Japanese Patent Laid-Open No. 2005-17782, Japanese Patent Laid-Open No. 8-292358 and Japanese Patent Laid-Open No. 2006-154373, a lead screw is provided in the driving mechanism part directly driven by a motor, and the motors and the lead screws are opposed to each other in parallel and coaxially with the optical axis, and it makes the total length in the optical axis direction long.
In the technology disclosed in Japanese Patent Laid-Open No. 8-271777, the motor and the lead screw are connected to each other by a transmission mechanism using a plurality of members, and it makes arrangement of the transmission mechanism difficult. Also, since the number of parts increases, it makes reduction of the size and weight difficult.
Also, in Japanese Patent Laid-Open No. 2006-64838 and Japanese Patent Laid-Open No. 2002-131611, driving force generation parts for driving two lens holders are arranged in parallel, and a motor, a drive shaft, and driving force transmission part (screw shaft, screw rod, etc.) are arranged coaxially. Therefore, the members are arranged in series in the optical axis direction, it is hard to make the length in the optical axis direction short.
That is to say, for the lens driving device in the conventional art, although the size in the width direction of the lens tube can be reduced, it has been difficult to reduce the size in the optical axis direction in the high ratio optical zooming. Also, to achieve size reduction, the number of parts for drive transmission may be increased and/or the arrangement of driving mechanism may be restricted.